A cloud‐resolving model study of aerosol‐cloud correlation in a pristine maritime environment

Abstract

AbstractIn convective clouds, satellite‐observed deepening or increased amount of clouds with increasing aerosol concentration has been reported and is sometimes interpreted as aerosol‐induced invigoration of the clouds. However, such correlations can be affected by meteorological factors that affect both aerosol and clouds, as well as observational issues. In this study, we examine the behavior in a 660 × 660 km2 region of the South Pacific during June 2007, previously found by Koren et al. (2014) to show strong correlation between cloud fraction, cloud top pressure, and aerosols, using a cloud‐resolving model with meteorological boundary conditions specified from a reanalysis. The model assumes constant aerosol loading, yet reproduces vigorous clouds at times of high real‐world aerosol concentrations. Days with high‐ and low‐aerosol loading exhibit deep‐convective and shallow clouds, respectively, in both observations and the simulation. Synoptic analysis shows that vigorous clouds occur at times of strong surface troughs, which are associated with high winds and advection of boundary layer air from the Southern Ocean where sea‐salt aerosol is abundant, thus accounting for the high correlation. Our model results show that aerosol‐cloud relationships can be explained by coexisting but independent wind‐aerosol and wind‐cloud relationships and that no cloud condensation nuclei effect is required.